cis-trans Isomers of PtX4L2 (X=halogen and L=neutral ligand): trans -bis(dimethyl sulfide)tetraiodidoplatinum(IV)

摘要

The octahedral title complex, [PtI4(C2H6S)2] or trans PtI4(dms)2 (dms is dimethylsulfide), crystallizes in the monoclinic space group P21/n (Z=2) with molecular symmetry Ci, which is the most frequently occurring point group for trans-PtX4L2[56%, 28 structures in the Cambridge Structural Database (CSD) [Allen, 2002, Acta Cryst B58, 380-388]] followed by C1 (22%, 11 structures). The complexes form a puckered pseudo-hexagonal layer in the (10-1) plane, and the layers are stacked with an interplanar distance of 7.10 Å. Density functional theory (DFT) calculations on an isolated complex with the observed parameters as a starting structure converged to C2h. Constraints to Ci on the observed geometry give 3-4 kJ mol-1 higher energy compared with C2h. DFT calculations on [PtCl4(PzH)2] (PzH is pyrazole), reported in the CSD in both the cis and trans forms, show an energy difference of 21 kJ mol-1 in favour of the trans complex. A CSD search for PtX4L2-type complexes, where X is a halogen and L is a ligand with a donor atom from group 14, 15 or 16, indicated a preferred trans geometrical arrangement, with a total fraction of 68%. The dominating crystal packing operators for the trans complexes are an inversion centre combined with a screw axis/glide plane (48%), followed by an inversion centre alone (28 %).